Chronic pain due to diabetic neuropathy and other causes can interfere with sleep, which carries a host of secondary complications. Transcutaneous electrical nerve stimulation (TENS) devices provide pain relief by stimulating sensory nerves, which leads to an increase in endogenous opioids and down-regulation of pain signal transmission to the brain.
The most common form of TENS is commonly referred to as “conventional TENS”. With a conventional TENS device, an electrical circuit generates stimulation current pulses with specified characteristics. The pulse waveform characteristics include intensity (mA), duration (μsec) and shape (typically monophasic or biphasic). The pulse pattern characteristics include the frequency (Hz) of the stimulation pulses and the length of each continuous stimulation session (minutes). These parameters are correlated to the therapeutic dose. For example, higher amplitude and longer pulses (i.e., larger pulse charge) increase the dose, whereas shorter stimulation sessions decrease the dose. Clinical studies suggest that pulse charge and stimulation session duration have the greatest impact on therapeutic dose.
Electrical stimulation is typically delivered to the user through electrodes, with the electrical stimulation being in the form of low intensity (typically less than 100 mA), short duration (typically 50-400 μsec) pulses at frequencies typically between about 10 and 200 Hz. The electrodes are placed on the skin of the user. The electrodes typically utilize hydrogels to create a stable low-impedance electrode-skin interface to facilitate the delivery of electrical current to the user so as to stimulate peripheral sensory nerves, whereby to suppress pain.
Poor sleep quality is one of the major causes of morbidity in patients suffering from chronic pain [Fishbain D A, Hall J, Meyers A L, Gonzales J, Mallinckrodt C. Does pain mediate the pain interference with sleep problem in chronic pain? Findings from studies for management of diabetic peripheral neuropathic pain with duloxetine. J Pain Symptom Manage. December 2008; 36(6):639-647]. It is, therefore, desirable for chronic pain sufferers to have the option of receiving TENS therapy during sleep. In fact, several studies have shown that TENS therapy can improve sleep quality (see, for example, Barbarisi M, Pace M C, Passavanti M B, et al. Pregabalin and transcutaneous electrical nerve stimulation for postherpetic neuralgia treatment. Clin J Pain. September 2010; 26(7):567-572).
A TENS device which could be used during sleep would offer unique opportunities to provide pain relief during bedtime with the goal of improving sleep. However, most TENS devices are designed to operate exclusively during the day (i.e., wake state) without any nighttime (i.e., sleep state) operation. This limitation is evident in the design of conventional TENS devices, in which the electric current is delivered by a stimulator through wires (called leads) that are connected to electrode pads on the skin. Such a design is not practical or safe for use during sleep because the leads are cumbersome and may get tangled or pulled, and because the electrode pads can potentially peel off the skin (which will terminate TENS therapy) or, perhaps worse, can potentially partially peel off the skin, leading to increased current density and negative consequences for the user (e.g., discomfort or, in extreme cases, burns).
In prior U.S. patent application Ser. No. 14/230,648, filed Mar. 31, 2014 by NeuroMetrix, Inc. and Shai Gozani et al. for DETECTING CUTANEOUS ELECTRODE PEELING USING ELECTRODE-SKIN IMPEDANCE, issued as U.S. Pat. No. 9,474,898 on Oct. 25, 2016, which patent is hereby incorporated herein by reference, there is disclosed a novel TENS device which allows TENS therapy to be applied during nighttime (i.e., during sleep state) as well as during the day (i.e., wake state). The key design elements that make this novel TENS device suitable for use during sleep are (1) the leads are eliminated because the electrode pads are attached directly to the housing containing the TENS stimulation circuitry, (2) the TENS housing and electrode pads are held reliably and comfortably against the skin by an adjustable strap or band, (3) the TENS device continuously measures skin-electrode contact impedance (and related electrical parameters) so as to detect if the electrode pads peel (completely or partially) off the skin and the TENS device stops delivering current if peeling is detected, (4) therapeutic stimulation may be scheduled in one-hour on-off blocks so as to provide pain relief throughout the night, and (5) the TENS device detects when the user is asleep and reduces the therapeutic stimulation level automatically so as not to disturb sleep.
The novel TENS device disclosed in prior U.S. patent application Ser. No. 14/230,648, filed Mar. 31, 2014 by NeuroMetrix, Inc. and Shai Gozani et al. for DETECTING CUTANEOUS ELECTRODE PEELING USING ELECTRODE-SKIN IMPEDANCE, issued as U.S. Pat. No. 9,474,898 on Oct. 25, 2016, which patent is hereby incorporated herein by reference, is designed to be located on the upper calf of the user. This is for three reasons. First, the TENS device needs to stimulate sensory nerve fibers in order to provide widespread pain relief through the systemic effect of an increase in endogenous opioids and down-regulation of pain signal transmission. The upper calf area has a cluster of sensory nerve fibers that can be activated easily with a transcutaneous electrical nerve stimulator because of their proximity to the surface of the skin. Second, some forms of chronic pain (such as that due to diabetic neuropathy) are experienced most acutely in the feet, and in addition to the mechanism of pain suppression through endogenous opioids described above (which is systemic), there is also evidence for additional mechanisms of pain suppression that are more local, thus making it advantageous to place the TENS device on the upper calf of the user. Third, chronic pain can be persistent throughout the day, often worsening at night, and wearing the TENS device on the upper calf makes it discreet and unobtrusive, which encourages more regular use.
In pending prior U.S. patent application Ser. No. 14/253,628, filed Apr. 15, 2014 by NeuroMetrix, Inc. and Shai Gozani et al. for TRANSCUTANEOUS ELECTRICAL NERVE STIMULATOR WITH AUTOMATIC DETECTION OF USER SLEEP-WAKE STATE, published as U.S. Patent Application Publication No. US 2014/0309709 on Oct. 16, 2014, which patent application is hereby incorporated herein by reference, there is disclosed a TENS device which is designed for use during sleep. This TENS device detects when the user is asleep and adjusts the therapeutic stimulation level to optimize therapy according to user preferences and simultaneously to avoid disturbing sleep.
In pending prior U.S. patent application Ser. No. 14/980,041, filed Dec. 28, 2015 by NeuroMetrix, Inc. and Thomas Ferree et al. for TRANSCUTANEOUS ELECTRICAL NERVE STIMULATOR WITH AUTOMATIC DETECTION OF LEG ORIENTATION AND LEG MOTION FOR ENHANCED SLEEP ANALYSIS, INCLUDING ENHANCED TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION (TENS) USING THE SAME, published as U.S. Patent Application Publication No. US 2016/0144174 on May 26, 2016, which patent application is hereby incorporated herein by reference, a novel TENS device is disclosed which may be used to improve sleep quality and to also quantify sleep quality and sleep disorders, since users will be more likely to use the TENS device if they are aware of, and convinced of, its benefit to their sleep.
The gold standard in determining the sleep-wake state of a subject is polysomnography which comprises at least three distinct types of data, i.e., electroencephalogram (EEG), electrooculography (EOG) and electromyography (EMG). Because of the difficulty in recording and analyzing these types of data, actigraphy has been developed and refined over the last 30 years as a practical alternative to study sleep/awake patterns. Actigraphy is a continuous recording of body movement by means of a body-worn device, typically equipped with accelerometers [Ancoli-Israel S, Cole R, Alessi C, Chambers M, Moorcroft W, Pollak C P. The role of actigraphy in the study of sleep and circadian rhythms. Sleep. May 1, 2003; 26(3):342-392].
Wearable electronic devices for health and fitness have become widespread, and most have accelerometers and, from acceleration data, compute various metrics of activity to track daytime activities and/or to quantify sleep patterns. Most of these actigraphy-based devices are worn on the wrist however, and in certain ways that limits their ability to detect and quantify sleep.
Significantly, it has now been recognized that the placement of a novel, accelerometer-equipped TENS device on the upper calf of a user, with tight mechanical coupling to the upper calf of the user, may be used to support novel approaches for detecting when the user is asleep, and novel metrics for analyzing the sleep of the user, and novel means to quantify body and leg motions associated with poor sleep quality and/or disorders such as restless leg syndrome, and novel methods for providing enhanced TENS therapy using the same. Among these novel metrics are “leg movements”, “body roll events” associated with rolling over in bed, and “time-on-back” data which is relevant to users suffering not only from chronic pain, but also from problematic sleep positions which can cause snoring or sleep apnea. In addition to tracking and reporting such sleep indicators, real-time feedback to the user, based on indicator trends, can also help the user to improve sleep quality. By way of example but not limitation, the novel device may be configured to provide an alert (e.g., via mechanical or electrical means on TENS device 100 or via a smartphone or another connected device) to the user when the time-on-back duration exceeds a threshold. By way of further example but not limitation, the novel device may be configured to modify TENS stimulation parameters when leg movement patterns associated with discomfort caused by nighttime pain are detected in order to enhance the analgesic effect of TENS therapy.